Xerographic developing apparatus



Feb. 25, 1964 J. J. GRIMM ETAL XEROGRAPHIC DEVELOPING APPARATUS 3 Sheets-Sheet 1 Filed Dec. 30, 1960 INVENTORS JAMES J. GR/HM BY HAROLD E. TRUMBULL TORNE Y Feb. 25, 1964 J, I M ETAL 3,122,454

XEROGRAPHIC DEVELOPING APPARATUS Filed Dec. 30, 1960 3 Sheets-Sheet 2 mmvroks JAMES J. GRIMM BY HAROLD E. TRUMBULL A T TORNEY Feb. 25, 1964 J. GRIMM ETAL 3,122,454

XEROGRAPHIC DEVELOPING APPARATUS Filed Dec. 30, 1960 3 Sheets-Sheet 3 INVENTORS JAMES J. GRIMM BY HAROLD E. TRUMBULL A TTOR/VE V 25, fidd i- 3,122,454 r :llQ BEVELGPING S lrlarol Trumbull, Qoluinbus,

J, Ser. No. 7?,dfill Cl. 118-637) This invention relates to xerography and, in particular to an improved apparatus for delivering developing material to a xerographic drum. More specifically the invention relates to an improved xerographic developing apparatus to effect cascade development of an electrostatic latent image on a xerographic drum.

in the process of xerography, for example, as disclosed in Carlson Patent 2,297,691, issued October 6, 1962, a Xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is ellected with an electrostatically charged, finely-divided material such as an lectroscopic p wder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electro static latent image. Thereafter, the developed xerographic powder image is usually transferred to a support surface to which it can be fixed by any suitable means.

ln automatic xerographic machines for the reproduction of copy, it is usual to utilize a constantly moving xerographic plate which may be in the form of a rotating cylindrical drumv By means of a continuously operative developing apparatus a developing material, of a type to be described, is constantly delivered to an upper portion of the drum surface to cascade down over the drum surface and then is retrieved by the developing apparatus. Since electrostatic latent images to be developed are produced on the drum surface in unrelated sequence or with an infinite variety of image configurations, it is important developing material be presented or delivered to the drum surface at a substantially uniform and adequate rate to effect image development.

Developing material for xerographic development may typically be of a two-component type as disclosed in Walkup l atent 2,638,416. The component materials of vValkup include a suitable pigmented or dyed electroscopic powder hereinafter referred to as toner and a granulated bead-like carrier, which later functions to carry and to generate triboelectric charges on the toner. More exactly, the function of the granular naterial is to provide the mechanical control to the powder, or to carry the powder to an image surface imultsmeously, to provide almost complete homogeneity or" charge polarity. In the development of the image, the toner is attracted to the drum surface in a pattern corresponding to the electrostatic latent image.

Developing apparatus for commercial automatic machines have heretofore been of a general type disclosed in copending application, Serial No. 393,058, filed November 19, 1953, in the name of Mayo et al. Typically this type of apparatus employs an endless conveyor-elevator which includes a plurality of drum-width buckets mounted on timing belts that are driven by specially adapted sprockets. A reservoir in the apparatus is filled with developing material "to above the lower level of the buckets so that they are filled passing through the material and are then elevated for delivery of the material to an upper portion of a xerographic drum.

Developing apparatus of the belt and bucket type have been successfully utilized in commercial machines. However, ecause of the inherent structural arrangement or the belt and bu t unit, certain problems have been encountered in their use for which solutions have heretofore not been found. For example, the lower sprockets of the conveyor are operated within the bull; or" the developing material and the action of the hard granular carrier beads thereagainst tends to quickly wear the inner surface of the belts which are a major first-cost factor. Also, as the buckets dig into the carrier beads they cause objectionable vibration and unless isolated has a deleterious effect on performing the other steps of the xerographic method that depend upon smooth performance of the apparatus to effect 0 eration. Additionally, the heretofore used apparatus has been known to be relatively noisy and relatively expensive to fabricate.

Any developing apparatus must have an inherent capacity for surhcient storage of developing material and must be capable of delivering an adequate amount of material at a substantially uniform rate. For example, in a typical application in which a drum has a perip ral rate of approximately 4 inches per s con-d, apprctely 3 pounds of developing material per minute is required to be delivered per inch of drum Width. Therefore, the apparatus should have sufficicnt storage capacity to cont" ually deliver the required amount. Preferably the apparatus should be 0 "ht weight construction, be quiet and sub stantially vibration free, and should contain and retrieve the material with a minimum of leakage. apparatus should also provide good mixing between the carrier beads and toner component of the developing material to effect the required t iboelectric properties.

Therefore, the principal object of the invention is to improve developing apparatus for delivering developing material to a xerographic drum.

Another object of the invention is to improve develop ing apparatus for substantially vibration free delivery or" developing material to a xerographic drum.

Still another object of the invention is to improve developing apparatus for delivering developing material to a xerograp'nic drum that is less expensive to fabricate than apparatus employed for the same purpose heretofore.

These and other objects of the invention are achieved by the novel developing apparatus of the invention which in the preferred embodiment includes a casing or housing having a wheel supported therein in position adjacent to a xerographic drum and adapted for approximately ver tical rotation with its axis arranged substantially at a right angle to the drum axis, a plurality of open buckets for conveying developing material upwardly supported on the wheel around its periphery with the bucket openings disposed toward the wheel axis, and a p of baffles one of which serves as a slide on which dc roping material can fall from substantially inverted position of the upper buckets to the drum surface for cascading thereover and the other of which serves as slide on which the cascaded material can descend from below the surface of the xerographic drum t the substantially upright posi tion of the l0\ 'er buckets. Sui able seals are provided for containing the material within 1e apparatus and a suitable toner dispenser is provided to replenish the developer material witi toner consumed in developing.

A preferred embodiment of tie invention is illustrated he accompanying drawings in whi 1 is a schematic illustration of a typical xerographic machine incorporating the developing apparatus of the invention;

FIG. 2 is a front elevation of the apparatus of the invention shown with a suitable type toner dispensing 3 apparatus, and partially broken away to facilitate understanding of its structure;

FIG. 3 is a sectional view taken on line 33 of FIG. 2;

FIG. 4 is a sectional elevation taken on line 4-'4 of FIG. 2; and,

FIG. 5 is an exploded isometric view of a drive arrangement to effect operation of both the apparatus of the invention and a type of toner dispenser which may be used in conjunction therewith.

General For a general understanding of the Xerographic processing system in which the invention is incorporated, reference is had to FIG. 1 in which the various system components are schematically illustrated. As in all Xerographic systems based on the concept disclosed in the above-cited Carlson patent, a radiation image of copy to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the electrostatic latent image is developed with an oppositely charged developing material to form a Xerographic powder image, corresponding to the electrostatic latent image, on the plate surface. The powder image is then usually transferred to a support surface to which it is fused by any suitable form of fusing device, whereby the powder image is caused permanently to adhere to the support surface.

The xerograpliic apparatus described herein typically may be of the type disclosed in the copending application, Serial No. 837,173, filed August 31, 1959, in the name of Cerasani et al. As in the apparatus thereof, original copy is placed on a support tray 1ft from which it is fed onto an endless conveyor 11 driven by motor 12. The conveyor moves the original past the optical axis of projection lens system 14 that is illuminated by a projection lamp LMP-l. The image of the original is reflected by mirror 15 through an adjustable objective lens 16, and then reflected by mirror 17 downwardly through a variable slit aperture assembly 1% onto the surface of a Xerographic plate in the form of drum 19.

Xerographic drum 19 includes a cylindrical member mounted in suitable bearings in the frame of the machine and is driven in a clockwise direction by a motor 24 at a constant rate that is proportional to the transport rate of the original copy, whereby the peripheral rate of the drum surface is identical to the rate of movement ofthe reflected radiation image. The drum surface comprises a layer of photoconductive material on a conductive backing that is sensitized prior to exposure by means of a screened corona generating device 25, which may be of the type disclosed in Walkup Patent 2,777,957, that is energized from a suitable high potential source (not shown).

The exposure of the drum to the radiation image discharges the photoconductive layer in the areas struck by radiation, whereby there remains on the drum a latent electrostatic image in image configuration corresponding to the radiation image projected from the original. As the drum surface continues its movement, the electrostatic latent image passes through a developing station 26 in which a two-component developing material 27, which may be of the type disclosed in the above-cited Walkup Patent 2,638,416, is cascaded over the drum surface by means of the developing apparatus generally designated 28, constructed in accordance with the invention.

After developing, the Xerographic powder image passes a discharge station 41 at which the drum surface'is illuminated by a lamp LMP-Z, whereby residual charges on the non-image areas of the drum surface are completely discharged. Thereafter, the powder image passes'through an image transfer station 42 at which the powder image is electrostatically transferred 'to. a support surface web araaaea similar to corona charging device The support surface to which the powder image is transferred may be of any convenient type, such as paper, and is fed from a supply roll 45 over guide rolls 46 and 47, being directed into surface contact with the drum in the immediate vicinity of transfer corona generating device as. After transfer, the support surface is separated from the drum surface and guided through a suitable fusing apparatus 48 which may be of the type disclosed in Crumrine Patent 2,852,651, whereby the powder image is permanently affixed to the support surface. Thereafter, the support surface is fed over a system of guide and tensioning rolls 49 onto a take-up roll 52 that is driven by means of motor 53.

After separation of the support surface from the drum,

a corona generathig device 54, which may be of the type described in copending application, Serial No. 845,482, filed October 9, 1959, in the name of Vyverberg, directs a negative charge to a residual powder image on the drum surface and to the support surface before leaving guide roll 4-7.

Thereafter, the xerographic drum surface passes through a cleaning station 55 at which its surface is brushed by a cleaning brush assembly 56, which includes a pair of brushes 59 and 60 rotated by a motor 57, whereby residual developing material remaining on the drum is removed. Thereafter, the drum surface passes through a second discharge station 58 at which it is illuminated by a fluorescent lamp LMP3, whereby the drum surface in this region is completely flooded with light to remove any electrostatic charge that may remain thereon. Suitable light traps (not shown) are provided in the system to prevent any light rays from reaching the drum surface, other than the projected image, duringthe period of drum travel immediately prior to sensitization by corona generating device 25 until after the drum surface is completely passed through the developing station 26.

Developing Apparatus Referring now to the subject matter of the invention,

the developer apparatus 28 includes a cylindrical housing to be positioned closely adjacent to the Xerographic drum.

Shitably secured to the outer faces of the side walls are a pair of seal holders 77 (see FIG. 3), also formed to conform with the shape ofthe drum, to support'seals 75,

preferably made of a self-lubricating material, and a resiL ient back support 76. The seals contact the outer peripheral edges of the drum to'form apowder tight seal between the developer assembly and the Xerographic drum. Secured to the top wall 72 is a gasket 73 adapted to cooperate with the enclosure (not shown) for the optical assembly of themachine to shield the drum from extraneous light.

For containing and delivering developer material to the Xerographic drum, there is-prouided a wheel type conveyor includ-ing'a circular disc 64 with a peripheral shell portion 83 formed integral-therewith, and pantly enclosed by annular ring 65. The wheel-type conveyor laterally extending vanes 66 suitably secured thereon, as by welding, forming open ended buckets for conveying developer rnaterialto the top o f'the developer housing.

For supporting the wheel conveyor assembly for rotation within the. housing, there'is'provided a flanged bearing support 92 sec-ured'to the rear Wall 69 of the deve loper housing. Thefianged bearingsupport extending through a suitable openingformed in the housing.

As seen in FIG. 4 the wheel conveyor is supported for rotation by a flanged hub sec d thereto and to one end of sleeve 39 that is jouinaled for rotation in the flanged bearings 93 positioned in the flanged bearing support. i suitable packing 9d 1 provided between these bearings. The wheel conveyor is maintained in axial alignment and is driven by spur gear 122 secured to the opposite end of sleeve The wheel conveyor is driven by means of motor 119 operatvely connected to drive shaft 12 by means of chain 117 which runs on sprockets lid and 11$ fixedly mounted on the shaft of motor 116 and to one end of drive shaft 125), respectively. The motor 11d, mounted by means of bracket to the housing 63, is connected to a source of electric power and is controlled by switching means (not shown). Drive shaft 12% is suit-ably journalcd and held in axial alignment in rear wall 69, and carries intermediate its ends a pinion gear 123 which meshes with the spur gear 122 to drive the wheel conveyor.

With a charge of developer material in the conveyor, the wheel-type conveyor is rotated and the developing n aterial begins spilling. The first spillage is baffled by carrier ring 103, secured to the toner dispenser and described in detail hereinafter, so as to cascade the spilled material over he toner dispenser into the lower buckets. eloping material which is further elevated ultimately spills into slide hopper or chute Ell -l secured to side wall 7-i and while gravitating down effects and triboelectrification between the toner and carrier particles which then pass through a preset openin' M for ed beabs tween the hopper and the shield section 7?; of the housing. The opening 195 is of a dimension to pass a requisite quantity of material and also to produce some backup accumulation and thereby eifect substantially uniform discharge of material across the axial width of the drum.

Thereafter, the developing mate l cascades down over the drum surface until being diverted by a return baffle lilo onto return or bottom wall bafile upon which the material descends into the buckets below. With the wheel in constant rotation there is constant delivery of developing material to above the hopper which through opening 1595 effects uniform delivery to the xerogr drum.

in a typical developing apparatus constructed in aid cordance with the invention and operated with a drum of approximately 4 inch dia eter and inch width, it

e was found that 3540 pounds of developing material could be delivered per minute to the drum by employing an 11 1 4 inch diameter wheel, 1 /2 inches wide, having 36 buckets, 1 inch deep. Delivery effected by rotating the wheel at approximately 48-52 r.p.m. whe leaded with an initial cl .rzc of l /22 pounds of mater The material passer through an opening of approximately wide and the entire apparatus was incli..ed toward the drum at approximately 6-10 degrees from the vertical. Cbviously th above values are typical and not be considered as lim t ng as various combinasions of s ced and dimension u ll produce the required rate of delivery for any particular application.

Dis ensiiig Apparatus As the developing mixture is cascaded over the xerographic drum, toner particles are pulled away from car icr and deposi ed on the drum to form powder images, Whhe the partly denuded carrier particles pass off the drum into the reservoir. As toner powder images are formed, addition l toner particles must be supplied to the dcvelopi g mxture in proportion to the amount of toner deposited on the drum. To supp-1y additional toner particles to the developing mixture, a toner dispenser is used to accirately meter toner to the developer mixture.

Alt' ough one or" a number of well-known powder or granulated material o ensers may be used, the toner enser shown is of the type disclosed in copending appnc on, Serial No. 79,702, filed concurrently herewith on December 30, 1960.

Referring now to the drawings the toner dispensing apatus includes a frustro-conical or cup-shaped res- 3 for the containment of toner material 112 to be dispensed and which is simply constructed and may, for example, be made of sheet metal stampings. Th6 reservoir conveniently is shaped as the frustrum of a cone and is mounted for rotation on horizontal shaft 84.

The reservoir is formed of a front section 96 and a rear wall 97 which is contiguously held, except as separated by disc 1-14, to the front section by means of brace 98 and screws 99 so as to provide a substantially powder tight n-"losure therebetween.

1 adding toner to the reservoir, there is provided a loading door 123 which pivots about hinges 124 secured to the front of the reservoir and is maintained in a closed position by resilient detent means 125. A plurality of keyslots 127 are provided whereby the drum can be retated by an operator to place the door into an upright position before opening.

Dispensing is eifected by means of a rotatable disk 114 which is supported to force a localized opening between front section 96 and rear wall 97 to produce localized opening. The disk may be plain or toothed and is journaled for rotation on a bent stub shaft secured, as by welding, to bottom wall 107. in the embodiment shown, the disk is approximately 2 inches in diameter and .605 inch Wide and as the reservoir rotates the disk is forced to rotate about its own fixed center by friction with the rear wall 97 and the open edge of front section The disk is located below the rotational axis of the reservoir and provides a fairly uniform slot opening at a point where dispensing occurs. Rotation of the disk effects a shearing action on the toner to keep it well mixed and also prevents toner bridging or agglomerating at the slot opening.

ine rate of (ll sensing by means of the apparatus of the invention is primarily a. function of the rotational rate of the reservoir although it is known that ambient conditions of temperature and humidity above standard atmosphere t t powder in a manner to impede dispensing.

iiv

sprocket HS mounted on shaft 14s suitably jo rear wall 69. Through pin 129 rotatably secured to the side face of sprocket 11S and to arm 133, the arm moves eccentrically as sprocket 113 is rotated. Movement of the arm 13% is transmitted as a cranking motion to plate 131, pivotably supported at one end on shaft 4, through pin 132 to move pawl 133 in an oscillatory motion. laWl 133 is secured to pin 141 which is rotatably secured to the end of plate and is normally biased into driving engagement with ratchet by means of spring 139. With each forward movement the pawl eng' es a tooth of ratchet 15d to effect its rotation and thro a which is rotated shaft 8 to which the dispen 'ng apparatus is secured.

Referring to FIGS. 4 and 5, shaft 84, carrying ratchet 134 fixed thereon, is journalcd for rotation with respect to sleeve by means of flanged ear' .gs positioned within t e sleeve. A packing H being inserted between the bear gs 9% The reservoir is secured to the front end of shaft 34 by means of hub Et 6 secured to the inner j by means of a segmental gear 135 supported loosely on shaft 84 which has a cam 136 extending therefrom to cover a toothed portion of ratchet 134. By means of handknob 137, connected to shaft 143 carrying worm gear 138 which meshes with gear 135, cam 36 is indexed to expose the ratchet tooth on which the pawl in its forward stroke first engages the ratchet. The pawl is urged downward by spring 1319 so as to successively ride the cam and then engage the ratchet. When the pawl engages the ratchet at the beginning of its forward stroke maximum rotation of the reservoir is effected, whereas pawl engagement with the ratchet near the end of stroke effects a minimum rotation of the reservoir. However, the absolute rates, i.e., the rotational displacement per unit of time diiiers by the relative angles of displacement after pawl engagement. As the reservoir rotates, disk 11 i rotates simultaneously therewith and it has been found that in addition to dispensing through the localized opening provided by the disk a minute amount of toner is carried and dispensed from the disk periphery.

Since the dispenser provided a uniform dispensing rate per unit of rotation, obviously other means such as a variable speed motor could be provided to vary the retational rate. As another alternative, different rates of dispensing uniformity can be effected by varying the dispensing opening as by movable wedge shaped disks or by using interchangeable disks of difierent dimensions.

Operation In operation, xerographic drum 19 is constantly rotated and an electrostatic latent image formed thereon passes through developing station 26 for developing the latent image by cascading a developing material thereover. Developing material is delivered to the drum for cascading by means of the improved developing apparatus 28 of the invention. In the developing apparatus, a supply of developing material is contained in the lower buckets. As the wheel rotates, the buckets containing the material are elevated until inverting and spilling the material onto slide-hopper 1%. On the hopper the material descends through opening 1&5 onto the drum to cascade thereover. The cascaded material is thereafter retrieved by means of baffles 1G6 and 107 which deflect the falling material into the upright buckets below. The cycle is continuous.

Toner consumed in the formation of powder images is replenished by means of dispensing apparatus 85. Dispensing is effected from a reservoir 113 through a localized open ng provided in the reservoir by a rotatable dispensing disk 114- and is achieved by rotating the reservoir. The dispensing rate can be regulated by means of a retatable cam 136 which changes the number of teeth in ratchet 134 picked up by constantly oscillating pawl 133 and varies the speed of the dispenser and consequently the dispensing rate.

By the apparatus above described there is disclosed a wheel type conveyor-elevatordeveloping apparatus for delivering developing material to a xerographic drum. The apparatus effects the required delivery and yet it is apparent that it is of simpler construction than apparatus employed heretofore. It has been found that fabrication cost of the present apparatus is approximately 55 percent of the previously used belt and bucket type mentioned above. The unit operates quietly and with a minimum of vibration.

Since many changes could be made in the above con struction and many apparently widely diiierent embodi ments of this invention could be made without departing from'the scope thereof, it is intended'tnat all matter contained in the drawings shall be interpreted as'illustrative and not in a limiting sense. 7

What is claimed is:

1. Apparatus for delivery of developing material to the peripheral surface of a xerographic drum, said apparatus including a housing supported adjacent a drum surface to aportiou ofwhich developing material is to be delivered, a wheel conveyor journaled for rotation in said housing, said wheel conveyor being adapted to con tain all of the material internally that is supplied to said rum surface and being mounted for rotation about an axis substantially perpendicular to the drum axis, said wheel conveyor having a plurality of open buckets capale of containing developing material, said buckets being supported on said wheel conveyor and arranged substantially concentric about the wheel conveyor axis with said bucket openings disposed radially to the axis of rotation of said wheel conveyor, means to rotate said wheel conveyor whereby material contained in the lower of said buckets is elevated from below to above said portion of the drum surface, a slide to convey developing material from the upper of said buckets to the drum surface to cascade thereover, means on said housing cooperable with said slide for controlling the flow of material across the axial width of the drum, and said housing having means to convey cascaded developing material from below the drum surface to the lower of said buckets.

2. The apparatus of claim 1 in which said wheel conveyor is positioned for rotation substantially in a vertical plane.

3. The apparatus of claim 1 in'which said wheel conveyor is positioned for rotation in a plane inclined from the vertical.

4. Apparatus for delivery of developer material to a portion of the periphery of a rotating xerographic drum, said apparatus including a housing supported adjacent the periphery of a rotating xerographic drum to which developer material is to be delivered, a wheel conveyor mounted in said housing, said wheel conveyor being adapted to contain all of the material internally that is supplied to said drum surface and being mounted for rotation about an axis substantiallyperpendicular to the drum axis, and including a plurality of open buckets for containing developer material, said buckets being supported in the wheel conveyor with the bucket openings disposed radially to said wheel conveyor axis, means to rotate said wheel whereby developer material contained in the lower of said buckets is elevated from below to above said portion of the drum surface, means to convey developer material from the upper of said buckets to the drum periphery to cascade thereover, means on said housing cooperable with said means to convey developer material for controlling the flow or" material across the axial width of the drum. and means to convey cascaded developer material from below the drum periphery to the lower of said buckets.

5. Apparatus for delivery of a developer material to a portion of the perishery of a xerographic drum being rotated about a substantially horizontal axis, said apparatusincluding the combination of a housing, a Wheel supported in said housing adjacent the periphery of a rotating xerographic drum to which the material is to be delivered, said wheel being adapted to contain all of the material internally that is supplied to said drum surface and being mounted for rotation about an axis substantially perpendicular to the drum axis, a plurality of open buckets capable-of containing developer material, said buckets being supported on said wheel with said bucket openings disposed radially to the axis of said wheel, means to rotate said wheel whereby developer. material contained in th lower of said buckets is elevated from below to above said portion of the drum surfaceQa first baiile means on which developer material descendsfrom the upper. of said-buckets to the periphery of the drum to cascade thereover, means onsaid housing cooperable with said first baffle means for controlling the flow of material across the axial Width of the drum, and second baffle means on which cascaded developer material from below the drum periphery descends to the lower buckets.

7 6. Apparatus for deliveryof developer material to a portion of the periphery of a rotating xerographic drum, said apparatus including thecombination of a casing, a

9 Wheel supported in said casing adjacent the periphery of a rotating Xerographic drum to which developer material is to be delivered, said wheel being adapted to contain all of the material internally that is supplied to said drum surface and being mounted for rotation about an axis substantially perpendicular to the drum axis, a plurality of open buckets capable of containing developer material, said buckets being supported on said Wheel and arranged with said bucket openings disposed radially toward said wheel axis, means to rotate said wheel whereby developer material contained in the lower of said buckets is elevated from below to above said portion of the drum surface, first baifie means on which developer material descends from the upper of said buckets to the periphery of the drum to cascade thereover, means on References Cited in the file of this patent UNITED STATES PATENTS 1,986,109 JoWett lian. 1, 1935 2,630,312 Carrier et al. Mar. 3, 1953 2,779,306 Dunn lan. 29, 1957 2,965,756 Vyverberg Dec. 20, 1960 2,990,278 Carlson June 27, 1961 3,011,474 Ulrich Dec. 5, 1961 

1. APPARATUS FOR DELIVERY OF DEVELOPING MATERIAL TO THE PERIPHERAL SURFACE OF A XEROGRAPHIC DRUM, SAID APPARATUS INCLUDING A HOUSING SUPPORTED ADJACENT A DRUM SURFACE TO A PORTION OF WHICH DEVELOPING MATERIAL IS TO BE DELIVERED, A WHEEL CONVEYOR JOURNALED FOR ROTATION IN SAID HOUSING, SAID WHEEL CONVEYOR BEING ADAPTED TO CONTAIN ALL OF THE MATERIAL INTERNALLY THAT IS SUPPLIED TO SAID DRUM SURFACE AND BEING MOUNTED FOR ROTATION ABOUT AN AXIS SUBSTANTIALLY PERPENDICULAR TO THE DRUM AXIS, SAID WHEEL CONVEYOR HAVING A PLURALITY OF OPEN BUCKETS CAPABLE OF CONTAINING DEVELOPING MATERIAL, SAID BUCKETS BEING SUPPORTED ON SAID WHEEL CONVEYOR AND ARRANGED SUBSTANTIALLY CONCENTRIC ABOUT THE WHEEL CONVEYOR AXIS WITH SAID 